Shear-resistant greases



Patented Sept. 28, 1948 SHEAR-RESISTANT GREASES Harry V. Ashburn,Glenham, Robert S. Barnett, Beacon, and Oney I. Puryear, Fishkill, N.Y., assignors to The Texas Company, New York, N. Y., a corporation ofDelaware No Drawing.

' This invention relates to improved lubricating grease compositions andparticularly to texturestable lithium base grease compositions in whicha synthetic oleaginous compound comprises part or all of the oilcomponent.

This is a continuation-in-part of our copending application Serial No.611,908, filed, August 21,

Recent developments in the production of lubricating greases andparticularly those designed for specialty equipment employing sealedbearings and operating over wide temperature ranges,- have led to theuse of a number of organic chemical compounds as substitutes for theconventional mineral lubricating oils, These oleaginous compounds offera marked advantage over the mineral oils in that they possess acomparatively uniform viscosity over a wide temperature range and arenot as susceptible to evaporation loss as a comparable viscosity mineraloil. These features are particularly desirable and have been used toadvantage in the production of greases used in sealed life-time bearinginstallations and low temperature greases used in aircraft controls andthe like. However, one undesirable characteristic of these so-calledsynthetic greases is their lack of resistance to shear. Under conditionsof operation where high shearing stresses are involved, such as in balland roller-bearing lubrication, the structure of these greases graduailybreaks down and their consistency falls off until they become liquid orsemi-liquid. At this point the greases no longer adhere to thelubricating surfaces and bearing failures result.

In accordance with the present invention it has been found possible toproduce a lithium base Application September 7, 1945, Serial No. 615,074

8 Claims. (Cl. 252--42.1)

grease compositions in which a synthetic oleaginous compound comprisespart or all of the oil component. The term "synthetic oleaginouscompound" as used herein embraces those organic compounds or mixturesthereof which possess lubricating qualities and may be substituted inwhole or in part for the conventional mineral lubricating oils. Thechoice of v the particular compounds used in the preparation of thesynthetic grease depends upon the type of lubricalion and thetemperature range within which the grease is intended to be operated. Ingeneral, these compounds are adapted to specialized lubrication outsidethe conventional lubricating temsynthetic grease composition whichpossesses not only the desirable characteristics-imparted by theoleaginous compounds, but is also resistant to shear. The syntheticgreases previously proposed and accepted by the industry have beenprepared from the lithium soaps of the conventional fatty acid sources,such as stearic acid and other soapforming fatty acids or theirglycerides. It has been discovered that the acid component of thelithium soap is an important factor in the production of syntheticgreases and that synthetic greases produced from lithium soaps ofsoapforming hydroxy fatty acids or their glycerides possess exceptionaltexture-stability and maintain their structure with little change inconsistency even after extensive working at either high or lowtemperatures.

This unusual characteristic of the lithium soaps of hydroxy fatty acidsis applicable to those perature ranges, such as ultra-low temperatureoperation found in refrigeration systems and arctic service lubrication,or to general purpose lubrication over a wide lubricating temperaturerange which was previously unattainable through the use of a singlemineral lubricating oil due to their high viscosity change over suchwide temperature ranges.

As a general proposition, certain factors are prerequisite in thecompounds falling within the category of synthetic oleaginous compounds.These compounds are necessarily chemically and physically stable liquidsat the temperatures of operation and possess a minimum viscosity of 0.5centistoke within the lubricating temperature range. Furthermore, thevapor pressure of these compounds in the lubricating temperature rangeis substantially negligible, although under conditions of floodedlubrication, where evaporation loss is not too critical, compounds ofmeasureable vapor pressure may be used,

' Inasmuch as the primary requisites of the oleaginous compounds arephysical in nature, they cannot be conclusively defined in terms oftheir chemical structure. However, the majority of these compounds arepolar compounds with oxygen as the principal type of polar constituent.Another general observation is that, in the compounds of a givenchemical classification, those of comparatively high molecular weightpossess the least change in viscosity per change in temperature. Thetypes of compounds which are recognized or have been proposed assynthetic oleaginous compounds include the aliphatic ethers, aromaticacid esters, aliphatic mono. and di-carboxylic acid esters, phosphorusacid esters,

and halogenated aromatic compounds. For the purposes of the presentinvention and as illustrative of the synthetic oleaginous compoundscontemplated by the invention, those compounds falling within thecategory of aliphatic dicarboxylic acid esters are preferred. Thecompounds within this particular class are the esters of such acids assebac c. adipic, pimelic, azelaic, alkenylsuccinic alkylma eic. etc, Theesters thereof are preferably the aliphatic esters and particularly thebranched chain aliphat cesters. Specific examples of the preferredoleaginous compounds are di-2-ethv hexyl sebacate. di-sec-amvl sebacate.di-2-ethylhexyl alkenylsuccinate. di-2-ethoxyethvl sebacate.di-2-(2'-methoxyethoxy) ethyl in the combination of mineral oil andoleaginous compound as the oil component of the finished "grease.

Furthermore, various addition agents may be incorporated with theoleacinous compounds to impart other desirable characteristics. Thus, anextreme pressure agent may be incorporated to improve the anti-wearcharacteristics of the compound or an anti-oxidant may be incorporatedtoimprove the anti-oxidant properties ofthe compound and/or the finishedgrease.

The lithium soaps which have been found to contribute to the desirableattributes of the s nthetic greases are those in which a, soap-forminghydroxy fatty acid constitutes at least part of the acid component. Thesoap-forming hydroxy fatty acids contemplated herein are thosecontaining at least 12 carbon atoms in the molecule and one or morehydroxyl groups. as well as mixtures thereof. These hydroxy fattyacidsmay be obtained from natural sources, such as castor oil, or may beprepared by the classical synthetic methods, such as oxidation ofunsaturated fatty acids or catalytic oxidation of petroleum oils andwaxes with extraction and fractionation to the whether or not mineraloil is to be used as part of the oil component; The conventional methodof preparing synthetic greases is the gelling method in which thepreformed lithium soap and the cleagincus compound are heated to ahomogeneous solution and rapidly cooled to form the grease gel. Thismethod of preparation possesses certain disadvantages in that itrequires a preformed lithium soap which in and of itself raises the costof the grease because of the separate saponification step required andextensive milling equipment to work the grease gel to a homogeneousconsistency. However, in preparing the greases of the invention othermethods of manufacture, conventional to the grease industry, may beused. A particular'advantage in the use of lithium soaps of hydroxyfatty acids is the fact that the high temperatures required by theconventional gelling methods may be avoided and the preparationconducted at temperatures around 300 F. or at least those attained in asteam-heated kettle and the finished grease drawn from the kettlewithout redesired molecular range. In the practice of the invention, asdescrimd herein, 12-hydroxy stearic acid and hydrogenated castor oilwill be used as the representative types of hydroxy fatty acids andtheir glycerides. These acids are preferred because of their advantageof availability and cost which renders them competitive to theconventional fats and fatty acids.

The soap-forming hydroxy fatty acids may be used as the sole acidiccomponent of the lithium soaps or they may be blended or combined withthe conventional fats or fatty acids in such proportions that at leastof the total acidic component is comprised of the hydroxy fatty acids.The choice of fats or fatty acids and the specific proportion thereofwhich may be blended or combined with the hydroxy fatty acids dependsupon the particular metallic constituent and the type of service forwhich the synthetic grease is intended. In general. any of therecognized fatty acid materials normally used in grease manufacture maybe used providing they are essentially saturated in character. Thesefats and fatty acids include mixtures of fatty acid glycerides found innaturally occurring fats and oils, together with fractionated componentsthereof. The fatty acids may be a mixture of acids split off from thesefats or prepared from hydrogenaquiring homogenization. Furthermore,saponification in situ is possible either in the presence of mineral oilor a synthetic oleaginous compound which is inert to the saponificationreaction.

The following examples are presented as illustrating the preparation ofrepresentative synthetic greases falling within the scope of the presentinvention. It is to be understood, however,

that these examples are merely illustrative and not definitive of theinvention and as suchmay be modified within the scope of the inventionas previously defined in accordance with the skill of the art.

Example I .hour and the kettle shut down over night. After standing overnight stirring at 35 R. P. M. was begun and the saponification mixturedehydrated at 290-312" F. for four hours. At this point the soap had avery light tan color. The heat was then reduced and 12.2 pounds ofmineral oil were added, The physical tests on th mineral oil andsynthetic 'oleaginous compound are as-follows:

Di-2-Ethyl- Mineral hexyl Sebaofl cate Flash, 000 "F Fire, 000 FViscosity Kinematic at F. m. Viscosity Kinematic at 210 F. cs. ViscosityIndex At 236F. grams of triple-pressed stearic "acid were added torender the grease slightly acidic. 26 pounds of di-Z-ethylhexyl sebacatewere then added slowly. At approximately 190 F. 36.60 pounds ofadditional di-2-ethylhexyl sebacate were added and during the additionof the ester 196.3 grams of phenyl alpha naphthylamine were addedsimultaneously. At this point the grease contained approximately 15%soap and possessed an A. S. T. M. penetration at 77 F. of 301-303unworked and 317-324 worked. 5 pounds of a blend of 28% mineral oil and72% sebacate ester and 23 grams of phenyl alpha naphthylamine were thenadded. The grease was finally drawn at a temperature of 166 F. andpumped through three 60 mesh screens. The product was a lightcream-colored buttery grease having the following calculatedcomposition: a

I Per cent Lithium soap (75% ydroxy stearic acid,

25% stearic acid) 13.6 Glycerlne 1.0 Mineral 011---; 23.8Di-Z-ethylhexyl sebacate 60.9 Phenyl alpha naphthylamine 05. Free fattyacid 0.2

' The foregoing synthetic grease was subjected to a dynamic shear testwhich was conducted in an apparatus consisting of a perforated pistonreciprocating within a, closed cylinder maintained at a constanttemperature. In the test the grease Example I! 6 grease-breakdownmachine wherein a No. 204 anti-friction bearing was packed with-thegrease and mounted-on a motor-driven shaft operating at 3450 R. P. M.and surrounded by a heatingjacket.. The test was started atroomtemperature and the bearing gradually .heated, while running at aconstant speed, until the temperature reached-300 lubricatingperformance was noted. -At the conclusion of the test the grease wasremoved from tho bearin .'and examined as to change in texture andconsistency. The results obtained on the subject grease indicatedexcellent lubrication, with no appreciable change in texture orconsistency of the grease at the. conclusion of the test.

In comparison therewith a commercial dimethyl silicone grease was alsotested and, although sup- A grease base consisting of the lithium soapsof the combination of 75% hydrogenated castor oil and 25% triple-pressedstearic acid and mineral oil was prepared in accordance with theprocedure of Example I. This grea'se' base possessed the followingcalculated composition:

Per cent Lithium soap 47.2 Glycerine 3.5 Mineral oil 49.3

750 grams of the grease base were charged to a kettle and heated withstirringat 234.F. The heat was then reduced and 1020 grams of a dimethylsilicone polymer possessing a flash point above 600 F., with a kinematicviscosity of 82 cs. at 100 F. and 32 cs. at 210 F. were slowly addedover a period of six and one-half hours. At this point the temperaturewas 147 F. and the A. S. T. M. control penetration at '77 was 203-210unworked and 221223 worked. 1000 grams of additional dimethyl siliconepolymer were then added slowly until a control worked penetration of 345at 78 F. was obtained. The batch was then drawn at a temperature of176F. The product was a smooth, light-colored, buttery grease having thefollowing calculated composition:

Per cent Lithium soap 12.8 Glycerlne 0.9 Mineral oil 13.4 Dimethylsilicone polymer 72.9

The subject grease was tested in.a so-called plying excellentlubrication, the grease became semi-fluid toward the end of the test anddrained from the bearing when the test was stopped.

Example III grams ,of lithium 12-hydroxy stearate and 900 grams ofdi-2-ethylhexyl sebacate were mixed I and heated with stirring. At 350Fjt-he'soap began to dissolve in the ester and at 390" F. was completelyin solution. The solution was heated to 400F. and poured in a thin layeron the bottom of a grease pan, taking care that no thick spots wereformed. After cooling, a smooth, but- I ,tery gel was formed whichshowed no signs of separation. The A. S. T. M. control workedpenetration of the grease gel was 240 at 77 F. The product possessed thefollowing calculated composition:

, Per cent Lithium 12-hy-droxy stearate--- 10 Di-Z-ethylhexyl sebacate90 This grease was tested in the dynamic shear test described in ExampleI in comparison witha 10% lithium stearate grease containing ell-2-ethylhexyl sebacate as the sole oil component and the results obtainedare as follows:

, Lithium I Lithium- Miniature Penetration Hydroxy Stearate stearateOriginal .Q 126, 181. Final 268, 270 Semi-fluid.

Where the said application Serial No. 611,908 discloses and claims alubricating grease composition of the synthetic ester typeof'lubricating base, together witha metal soap of hydroxy fatty acids orhydroxy fatty acid glycerides, and specificallya sodium soap grease ofthis type, the present application is restricted to a lithium soapgrease of this general type.

Obviously many modifications and variations to thicken said lubricantbase, said soap-forming F. During the period of the test the e 7 fattymaterial consisting of more than 50% by weight of a hydroxysoap-forming-fatty material selected from the group consisting ofhydroxy fatty acids and hydroxy fatty acid glycerides, said greasecomposition being texture-stable under high shearing stress.

2. A lubricating grease composition according to claim 1, wherein thesaid ester is a branched chain aliphatic diester of an aliphatic'dicarboxylio acid.

3. A grease composition according to claim 2,

wherein the said ester is a branched chain aliphatic sebacate.

4. A lubricating grease composition according to claim 3, wherein thesaid diester is di-z-ethyl hexyl sebacate.

5. A lubricating grease composition comprising as the major portion ofthe composition a lubricant base consisting of a minor proportion ofmineral lubricating oil and a major proportion of an oil-soluble highmolecular weight high boilin liquid branched chain aliphatic dies'ter ofan allphatic .dicarboxyiic acid, sufficient lithium soap of asoap-forming fatty material consisting of a major proportion ofhydrogenated castor oil and a minor proportion of a saturatedsoap-forming fatty acid to thicken said lubricant base, glycerineresulting from the saponification of said hydrogenated castor oil, and asmall proportion of an oxidation inhibitor, said grease compositionbeing texture-stable under high shearing stress.

6. A lubricating grease composition according to claim 5, wherein saiddiester is di-2-ethy1 hexyl sebacate.

7. A lubricating grease composition comprising as the major portion ofthe composition a lubricant base consisting of a minor proportion ofmineral lubricating oil and a major proportion of 8 an oil-soluble highmolecular weight high boiling liquid branched chain aliphatic dies-terof an aliphatic dicarboxylic acid, sufficient lithium soap of about a3:1 mixture by weight of hydrogenated castor oil and stearic acid tothicken said lubri= cant base, glycerine, and a small proportion of anREFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,993,738 Graves et al Mar. 12,1935 2,049,072 Mikeska July 28, 1936 2,104,408 Wiezevich Jan. 4, 19382,303,256 'Camelford Nov. 24, 1942 2,334,274 Meadows Nov. 16, 19432,351,384 Woods et al June 13, 1944 2,376,312 Morgan May 15, 19452,379,850 Morgan July 3, 1945 2,380,960 Fraser Aug. 7, 1945 2,383,147Morgan Aug. 21, 1945 2,390,450 Morgan Dec. 4, 1945 2,397,956 Fraser Apr.9, 1946 FOREIGN PATENTS Number Country Date 406,136 Great Britain Feb.22, 1934 157,953

Switzerland Jan. 2, 1933

